This invention relates to drive transmission mechanism for a four-wheel-drive tractor where the dirigible front wheels as well as the rear wheels are all of drivable construction and a power-take-off shaft is provided in a rear portion of the transmission housing which bears the rear wheel assembly.
It is generally the practice in four-wheel-drive tractors, for properly adapting the rotation speed of the front wheels to that of the rear wheels, to transmit to the front wheels the power taken out from rear end of the rear-wheel-driving main gearing shaft assembly, and there has conventionally been adopted the construction where a long transmission shaft extending from the rear end of the main gearing shaft assembly to the front wheels is suspended in a space under the vehicle body. It has thus been hard to provide sufficient empty space height above the ground in the underbelly portion of the tractor. Moreover, as the transmission shaft becomes inevitably long, the shaft must be of large diameter for realizing sufficient transmission strength, thus making the space in the underbelly portion of the tractor all the more narrower, and adoption of the large-diameter shaft incurs increase in weight as well.
Incidentally, when the power-take-off shaft is provided in the rear portion of the transmission housing, the drive assembly is needed in addition to running travel gearing shaft assembly in the transmission housing, thus apt generally to require larger transmission housing because of the increased number of the accommodated shafts. When the housing becomes thus larger, it is preferable to provide entirety of such housing as low as possible for stability of the vehicle, but such contradicts securing sufficient height of empty space below the underbelly of the vehicle body.